The spleen is the largest organ of the immune system. It is located in the left side of the upper abdomen. It is mostly composed of two main structures that are specialized in immune response and in blood filtration. These two structures are called the white pulp and the red pulp. The white pulp is specialized for immune response and is composed of lymphatic tissue, mostly lymphocytes. The red pulp has a function related to blood cells in the circulation.
The outer layer of the spleen is called the capsule which is made of dense connective tissue that contain contractile cells. These cells when contracted help in ejecting blood from the spleen to the outer circulation.
The spleen is characterized by its rich supply in blood and lymphocytes. The hilum in the spleen is the site of passage for the splenic artery and vein.
The functions of the spleen include two main categories. These are functions on the immune level and function on the blood cells level. On the immune level the spleen has several function. They include: The presentation of antigens in the circulation using antigen presenting cells found in the spleen and thus starting an appropriate immune response.
The spleen is also the site for T and B lymphocytes derivation. It is also responsible for producing antibodies against antigens found in the blood.
What so far has been mentioned about the spleen function had to do with its immunologic function. We turn now to its function with regard to red blood cells filtration. These functions include the destruction of aged and damaged erythrocytes and platelets.
It functions also by recycling the iron metal from damaged erythrocytes hemoglobin. In addition to these functions, it has an important function in fetal life, in which it is the site of red blood cells formation.
The spleen is as was mentioned previously is rich in blood supply. Therefore it is a reservoir for blood that are expelled from the spleen to the circulation after the contraction of the cells of the capsule of the spleen.
The main disorder of the spleen that is found in clinical practice is splenomegaly or enlarged spleen. There are many causes which can cause enlarged spleen. The normal spleen cannot be detected on physical examination but the enlarged spleen can.
The causes of enlarged spleen can be divided as neoplastic or malignant and non-neoplastic or nonmalignant causes. Examples of non-neoplastic causes include infectious diseases such as infectious mononucleosis and malaria.
Autoimmune diseases can cause enlarged spleen as well such as Rheumatoid arthritis and lupus erythematusus. A liver disease that is called cirrhosis causes also an enlarged spleen. There are a group of neoplastic conditions that cause enlarged spleen. Among them is leukemia and in particular chronic lymphocytic leukemia. Another malignant condition that causes enlarged spleen is called polycythemia vera. This condition has to do with a blood malignancy.
The cure is splenectomy. The individual can live with and without a spleen. Therefor the spleen is not an essential organ for humans life.